The present invention pertains to the mechanism for retaining a tool holder in the socket of a machine tool spindle, ejecting it therefrom for removal from the machine and cleaning chips and debris from the socket and tool holder during the tool change cycle.
With the advent of automatic tool changers for changing the tools in the socket of a machine tool spindle, the need arose for an automatic power operated mechanism to retain the tool in the socket of the spindle and to eject the tool when it is desired to remove the tool from the machine. A variety of mechanisms have been devised to meet this need. Most of them require the boring of a hole through the entire length of the spindle along its axis for the reception of a drawbar that actuates the collet mechanism for securing the tool. With this arrangement the source of power for actuating the drawbar is mounted at the back end of the spindle. Such mechanism increases the length of the space required for the spindle. Moreover, the bore extending through the length of the spindle reduces its strength so that a larger diameter spindle is required.
An example of the prior art tool retention mechanisms is illustrated in U.S. Pat. No. 4,347,753 where the actuating mechanism is shown mounted on the rear end of the spindle to add a substantial length to the spindle. Moreover, the actuating mechanism actuates a control bar that extends through the entire length of the spindle requiring a relatively large axial bore in the spindle.
Such disadvantages in power operated drawbars for a tool retention and ejection mechanism were overcome by the structure depicted in U.S. Pat. No. 4,632,613 where the power for operating the drawbar is obtained from an annular piston and cylinder mechanism disposed in an annular space between the spindle and the quill that supports the spindle. This eliminates the power source mounted on the end of the spindle and does not require the axial bore through the entire length of the spindle. However, the mechanism employs a plurality of pins extending radially in the spindle and movable axially to engage the retention knob of a conventional tool holder for retaining the tool holder in the spindle socket and for ejecting it therefrom. This design has been found to be lacking in reliability because of the failure of the pins due to rapid wear and distortion. The mechanism is also very sensitive to inaccuracies in construction and the radial holes that are required in the spindle to accommodate the pins detract from the strength of the spindle. Moreover, the radial holes are required in the area of the spindle bearings so that the two bearings cannot be spaced from each other to increase the rigidity of the spindle.